6 EXPERIMENTAL POLLINATION. 



widely removed in time and space will differ much in detail and often in 

 principle as well. 



Normal pollination. — This is primarily a matter of observation and 

 is important in experimental studies chiefly because it furnishes a back- 

 ground of normal behavior against which departures may be measured. 

 The methods are simple and have long been exemplified in the works of 

 Delpino, Hildebrand, Axell, Mueller, Darwin, Kerner, Knuth, Loew, 

 MacLeod, Robertson, and others. For the more exact results needed in 

 connection with experiments, it has proved necessary to enter into finer 

 details as to behavior, to deal with a larger number of individuals, and 

 especially to record the number of visitors of each species, as well as the 

 number of flowers visited by each individual. The failure to note the 

 number of visitors of each species deprives practically all of the observa- 

 tional studies of any quantitative value, in spite of the contention of Knuth 

 (1906:195) that the "statistical" method of Mueller has greater possi- 

 bilities than one would be inclined to believe and that the reproach of 

 affording an inaccurate idea of the number of pollinators because it counts 

 the visits of species and not of individuals is of no importance. This is 

 contradicted by the earlier statement that 'a disadvantage is involved, 

 though one that can hardly be avoided, as it is almost impossible to count 

 all the individual visits to a conspicuous flower.' 



In a critique of Knuth's "Bliitenbiologie," Roberston (1922:148) states 

 that anthecological data "are lists of insect visitors made to show the 

 species, their frequency, their efficiency as pollinators, and the possibility 

 of their having some influence in determining the characters of the flowers. 

 Mueller's lists show these details. In the case of the bees he indicated 

 the sexes, and whether they were sucking nectar or collecting pollen. To 

 note the sexes is important, because female bees fly longer than males and 

 are more likely to make repeated visits. To note the fact of pollen- 

 collecting is also important. A female bee will carry pollen all day from 

 flowers on which the male rarely occurs. From observations at Carlinville 

 the females of nest-making bees average 20.6 visits to the males 10.3. The 

 inquiline bees show females 8.8 to males 8.0. In anthecology Mueller's 

 lists are valuable as regards species and visits, but they fail to indicate the 

 frequency. In 1908 I rejected Mueller's method and adopted the practice 

 of capturing the individuals as they came, noting species and counting 

 individuals It is impossible to indicate the importance of insects to flowers 

 by lists of species, because efforts to increase the lists involve an exaggera- 

 tion of the importance of rare and exceptional cases." 



Experimental pollination. — This includes practically all the experi- 

 mental methods that deal with the relations of flowers and insects, though 

 competitive methods are considered separately for the sake of convenience. 

 No sharp line can be drawn between these and the methods that make use 

 of colored objects or odorous substances, but it seems better to consider 

 the latter in a separate section. Experiments may be devised to show 

 the role of different parts in attraction, landing, or guidance, the behavior 

 of insects in securing nectar or pollen, or their efficiency in the transfer of 

 pollen. However, in many cases two or more of these processes are affected 



